The invention relates to the structure of a lifting head coupled to a swivel arm of an assembly robot or the like.
In a swivel-arm type assembly robot, the swivel arm has a chuck mounted at the end thereof. The chuck is supported by a lifting shaft which is rotatable. The lifting shaft is turned and moved vertically to supply or assemble workpieces or parts. If it is required to perform rotation and vertical movement with high positioning accuracy, the chuck is driven by a servo-controlled feed screw or drive motor.
However, if a feed screw mechanism or driven motor is installed on the head of the swivel arm, the total weight of the head is significantly increased, and therefore the movement of the robot becomes slow and the maximum weight of a part or workpiece carried thereby is limited. Accordingly, the weight of such a lifting head should be reduced as much as possible.
In order to satisfy this requirement, the present applicant has proposed a so-called "double-support structure" in which a vertical feed screw is rotatably supported with respect to the head, and the upper end portion of the feed screw is rotatably supported by a part of the casing. However, this structure still suffers from the difficulties that, as the vertical stroke increases, the positioning accuracy drops, and it is rather difficult to significantly reduce its weight.
In the use of a fluid-operated chuck, a pipe extending from the robot body must be connected to the chuck. In the case where the pipe is connected directly to the side of the chucks, the lift and rotation of the chuck are limited thereby, and therefore it is preferable to restrict the passages to inside the lifting shaft. In such a case, the fluid passage is communicated through the pipe with the robot body.
As the lifting shaft is moved up and down, the pipe is also, may strike the cover, etc., and a component of the force in the direction of the pipe exerted on the lifting shaft, thus lowering the positioning accuracy.